In the photofinishing of photosensitive material, reels of heat-spliced undeveloped filmstrips are run through high speed, chemical film processors in a light-tight environment. Occasionally, the film web breaks in the processing apparatus, sounding an alarm to the operator. The operator then quickly splices the broken end together with metal staples so as not to affect the chemical processing of the film and productivity. At the output of the machine, the processed web is again wound on a reel to be used in other photofinishing devices, for example, a printer. Usually the metal staples are removed from the reel and a heat-splice is inserted in its place, thus preventing any damage to downstream devices, such as printers, finishing stations, etc. On occasion, the staples are not removed, in which case, an automatic detection scheme is needed to detect a staple in the downstream device and stop the film web before the staples do damage to the downstream device. This problem has become even more critical with respect to recently developed film containing magnetic information thereon. An example of such films are disclosed in U.S. Pat. Nos. 4,933,780 and 5,016,030. Typically, devices are used to either read and/or write information onto a thin magnetic layer provided on the film. These magnetic devices are very sensitive, and can be damaged easily by the passing of a staple across the surface. An example of downstream a device is the film prep workstation disclosed and described in U.S. Ser. No. 08/394,533, filed Feb. 17, 1995, entitled FILM PREPARATION WORKSTATION, by Bradley C. DeCook and Thomas J. Murray. Magnetic read/write devices may also be placed in various printers and finishing devices for providing information and/or reading information therefrom. Thus, it has become even more important to detect the staples prior to the insertion of the film into the device. In addition, it is important that the method used for detecting the staples not interfere with the devices used. Because of the close proximity of the magnetic read and/or write heads, it is important that the staple detection mechanism have low EMI noise so as to not interfere with the magnetic write and/or read heads.
Present methods of detecting staples in spliced filmstrips require a mechanical set-up gap to monitor the thickness of the film as it passes therethrough. The setting for the gap must be set for the smallest anticipated film plus staple dimension, so as to mechanically stop the film motion. However, misalignment of the detector permits staples to pass, which may result in damage to downstream devices.
The present invention provides a low cost, reliable method for monitoring metallic staples in a web, which also produces low EMI noise, thereby minimizing any potential interference with other electrical devices that may be present.